1. Field of the Invention
This invention relates to a method of controlling an engine speed for an internal combustion engine and an apparatus therefor, and more particularly to a method for controlling the speed or number of revolutions of an internal combustion engine to a predetermined or set level or engine speed and an apparatus therefor.
2. Description of the Prior Art
A control system of such type which has been conventionally known and practiced in the art is generally adapted to allow proportional control action to operate an engine speed adjusting operation unit in view of deviation of the actual engine speed of an engine from a predetermined or set engine speed thereof and allow derivative control action to operate the operation unit dependent upon the rate of change of the actual engine speed with respect to time, to thereby keep the actual engine speed at the set value. The term "operation unit" used herein indicates, for example, a throttle valve in a gasoline engine or an injection adjusting means of a fuel injection pump in a diesel engine. In such conventional control system, when the engine speed changes in the direction away from the set value, the proportional action and derivative action act together to return the engine speed to the set value; however, once the engine speed begins to change in the direction toward the set value, only the proportional action takes place to return the engine speed to the set value and the derivative action acts to restrain the engine speed from approaching the set value. In view of the foregoing, the conventional system is constructed to carry out the derivative action over the whole range of change of the engine speed, thus, it has an important disadvantage that it takes too much time to return the actual engine speed to the set value to cause transient response characteristics to be substantially deteriorated, when a load of the engine varies and/or the set value is changed.